Color stable red-emitting phosphors

ABSTRACT

A lighting apparatus includes a semiconductor light source in direct contact with a polymer composite comprising a color stable Mn4+ doped phosphor, wherein the lighting apparatus has a color shift of ≤1.5 MacAdam ellipses after operating for at least 2,000 hour at a LED current density greater than 2 A/cm2, a LED wall-plug efficiency greater than 40%, and a board temperature greater than 25° C.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/285,746, filed on May 23, 2014, now copending, which is acontinuation of International Application No. PCT/US2014/027733, with aninternational filing date of Mar. 14, 2014, which claims the benefit ofU.S. Provisional Application No. 61/791,511, filed on Mar. 15, 2013, theentire disclosures of which are incorporated herein by reference.

BACKGROUND

Red-emitting phosphors based on complex fluoride materials activated byMn⁴⁺, such as those described in U.S. Pat. Nos. 7,358,542, 7,497,973,and 7,648,649, can be utilized in combination with yellow/green emittingphosphors such as YAG:Ce or other garnet compositions to achieve warmwhite light (CCTs<5000 K on the blackbody locus, color rendering index(CRI) >80) from a blue LED, equivalent to that produced by currentfluorescent, incandescent and halogen lamps. These materials absorb bluelight strongly and efficiently emit between about 610-635 nm with littledeep red/NIR emission. Therefore, luminous efficacy is maximizedcompared to red phosphors that have significant emission in the deeperred where eye sensitivity is poor. Quantum efficiency can exceed 85%under blue (440-460 nm) excitation.

While the efficacy and CRI of lighting systems using Mn⁴⁺ doped fluoridehosts can be quite high, one potential limitation is theirsusceptibility to degradation under high temperature and humidity (HTHH)conditions. It is possible to reduce this degradation usingpost-synthesis processing steps, as described in U.S. Pat. No.8,252,613. However, further improvement in stability of the materials isdesirable.

BRIEF DESCRIPTION

Briefly, in one aspect, the present invention relates to a process forsynthesizing a color stable Mn⁴⁺ doped phosphor. A precursor of formulaI is contacted with a fluorine-containing oxidizing agent in gaseousform at an elevated temperature to form the color stable Mn⁴⁺ dopedphosphor

A_(x) [MF_(y)]:Mn⁴⁺

wherein

-   -   A is Li, Na, K, Rb, Cs, NR4 or a combination thereof;    -   M is Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Hf, Y, La, Nb, Ta, Bi,        Gd, or a combination thereof;    -   R is H, lower alkyl, or a combination thereof;    -   x is the absolute value of the charge of the [MF_(y)] ion;    -   y is 5, 6 or 7;    -   the temperature ranges from about 200° C. to about 700° C.; and    -   the fluorine-containing oxidizing agent is F₂, anhydrous HF,        BrF₅, NH₄HF₂, NH₄F, AlF₃, SF₆, SbF₅, ClF₃, BrF₃, KrF, XeF₂,        XeF₄, NF₃, PbF₂, ZnF₂, SiF₄, SnF₂, CdF₂ or a combination        thereof.

In another aspect, the present invention relates to color stable Mn⁴⁺doped phosphors that may be produced by the process.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a schematic cross-sectional view of a lighting apparatus inaccordance with one embodiment of the invention;

FIG. 2 is a schematic cross-sectional view of a lighting apparatus inaccordance with another embodiment of the invention;

FIG. 3 is a schematic cross-sectional view of a lighting apparatus inaccordance with yet another embodiment of the invention;

FIG. 4 is a cutaway side perspective view of a lighting apparatus inaccordance with one embodiment of the invention;

FIG. 5 is a schematic perspective view of a surface-mounted device (SMD)backlight LED.

DETAILED DESCRIPTION

In the processes according to the present invention, a non-color stableprecursor to a color stable phosphor is annealed, or subjected to anelevated temperature, while in contact with an atmosphere containing afluorine-containing oxidizing agent. The precursor is a complex fluoridematerial activated by Mn⁴⁺ of formula I. In the context of the presentinvention, the term “complex fluoride material or phosphor”, means acoordination compound, containing at least one coordination center,surrounded by fluoride ions acting as ligands, and charge-compensated bycounter ions as necessary. In one example, K₂SiF₆:Mn⁴⁺, the coordinationcenter is Si and the counterion is K. Complex fluorides are occasionallywritten down as a combination of simple, binary fluorides but such arepresentation does not indicate the coordination number for the ligandsaround the coordination center. The square brackets (occasionallyomitted for simplicity) indicate that the complex ion they encompass isa new chemical species, different from the simple fluoride ion. Theactivator ion (Mn⁴⁺) also acts as a coordination center, substitutingpart of the centers of the host lattice, for example, Si. The hostlattice (including the counter ions) may further modify the excitationand emission properties of the activator ion.

The non-color stable precursor has a nominal composition similar to thecolor stable phosphor but lacks the color stability of the finalproduct. The amount of manganese in the Mn⁴⁺ doped precursors of formulaI and in the color stable phosphors ranges from about 0.3 weight % toabout 1.5 weight %, based on total weight of the precursor or colorstable phosphor. K₂SiF₆:Mn⁴⁺ containing about 0.5 wt % Mn, before andafter annealing, is typically more color stable under high light fluxconditions than K₂SiF₆:Mn⁴⁺ containing about 0.68 wt % Mn, before andafter annealing. For K₂SiF₆:Mn⁴⁺, the amount of Mn ranges from about0.50 wt % to about 0.85 wt %, more particularly from about 0.65 wt % toabout 0.75 wt %.

In particular embodiments, the coordination center of the precursor,that is, M in formula I, is Si, Ge, Sn, Ti, Zr, or a combinationthereof. More particularly, the coordination center is Si, Ge, Ti, or acombination thereof, and the counterion, or A in formula I, is Na, K,Rb, Cs, or a combination thereof, and y is 6. Examples of precursors offormula I include K₂[SiF₆]:Mn⁴⁺, K₂[TiF₆]:Mn⁴⁺, K₂[SnF₆]:Mn⁴⁺,Cs₂[TiF₆], Rb₂[TiF₆], Cs₂[SiF₆], Rb₂[SiF₆], Na₂[TiF₆]:Mn⁴⁺,Na₂[ZrF₆]:Mn⁴⁺, K₃[ZrF₇]:Mn⁴⁺, K₃[BiF₆]:Mn⁴⁺, K₃[YF₆]:Mn⁴⁺,K₃[LaF₆]:Mn⁴⁺, K₃[GdF₆]:Mn⁴⁺, K₃[NbF₇]:Mn⁴⁺, K₃[TaF₇]:Mn⁴⁺. Inparticular embodiments, the precursor of formula I is K₂SiF₆: Mn⁴⁺.

Although the inventors do not wish to be held to any particular theoryto explain the improvement in color stability that can result fromsubjecting the precursor to a process according to the presentinvention, it is postulated that the precursor may contain defects suchas dislocations, F⁻ vacancies, cation vacancies, Mn³⁺ ions, Mn²⁺ ions,OH⁻ replacement of F⁻, or surface or interstitial H⁺/OH⁻ groups thatprovide non-radiative recombination pathways, and these are healed orremoved by exposure to the oxidizing agent at elevated temperature.

The temperature at which the precursor is contacted with thefluorine-containing oxidizing agent may range from about 200° C. toabout 700° C., particularly from about 350° C. to about 600° C. duringcontact, and in some embodiments from about 200° C. to about 700° C. Invarious embodiments of the present invention, the temperature is atleast 100° C., particularly at least 225° C., and more particularly atleast 350° C. The phosphor precursor is contacted with the oxidizingagent for a period of time sufficient to convert it to a color stablephosphor. Time and temperature are interrelated, and may be adjustedtogether, for example, increasing time while reducing temperature, orincreasing temperature while reducing time. In particular embodiments,the time is at least one hour, particularly for at least four hours,more particularly at least six hours, and most particularly at leasteight hours. In a specific embodiment, the precursor is contacted withthe oxidizing agent for a period of at least eight hours and atemperature of at least 250° C., for example, at about 250° C. for aboutfour hours and then at a temperature of about 350° C. for about fourhours.

The fluorine-containing oxidizing agent may be F₂, HF, SF₆, BrF₅,NH₄HF₂, NH₄F, KF, AlF₃, SbF₅, ClF₃, BrF₃KrF, XeF₂, XeF₄, NF₃, SiF₄,PbF₂, ZnF₂, SnF₂, CdF₂ or a combination thereof. In particularembodiments, the fluorine-containing oxidizing agent is F₂. The amountof oxidizing agent in the atmosphere may be varied to obtain the colorstable phosphor, particularly in conjunction with variation of time andtemperature. Where the fluorine-containing oxidizing agent is F₂, theatmosphere may include at least 0.5% F₂, although a lower concentrationmay be effective in some embodiments. In particular the atmosphere mayinclude at least 5% F₂ and more particularly at least 20% F₂. Theatmosphere may additionally include nitrogen, helium, neon, argon,krypton, xenon, in any combination with the fluorine-containingoxidizing agent. In particular embodiments, the atmosphere is composedof about 20% F₂ and about 80% nitrogen.

The manner of contacting the precursor with the fluorine-containingoxidizing agent is not critical and may be accomplished in any waysufficient to convert the precursor to a color stable phosphor havingthe desired properties. In some embodiments, the chamber containing theprecursor may be dosed and then sealed such that an overpressuredevelops as the chamber is heated, and in others, the fluorine andnitrogen mixture is flowed throughout the anneal process ensuring a moreuniform pressure. In some embodiments, an additional dose of thefluorine-containing oxidizing agent may be introduced after a period oftime.

In another aspect, the present invention relates to a process forsynthesizing a color stable Mn⁴⁺ doped phosphor, the process comprisingcontacting a precursor at an elevated temperature with afluorine-containing oxidizing agent in gaseous form to form the colorstable Mn⁴⁺ doped phosphor, wherein the precursor is selected from thegroup consisting of

-   -   (A) A₂[MF₅]:Mn⁴⁺, where A is selected from Li, Na, K, Rb, Cs,        NH₄, and combinations thereof; and where M is selected from Al,        Ga, In, and combinations thereof;    -   (B) A₃[MF₆]:Mn⁴⁺, where A is selected from Li, Na, K, Rb, Cs,        NH₄, and combinations thereof; and where M is selected from Al,        Ga, In, and combinations thereof;    -   (C) Zn₂[MF₇]:Mn⁴⁺, where M is selected from Al, Ga, In, and        combinations thereof;    -   (D) A[In₂F₇]:Mn⁴⁺ where A is selected from Li, Na, K, Rb, Cs,        NH₄, and combinations thereof;    -   (E) A₂[MF₆]:Mn⁴⁺, where A is selected from Li, Na, K, Rb, Cs,        NH₄, and combinations thereof; and where M is selected from Ge,        Si, Sn, Ti, Zr, and combinations thereof;    -   (F) E[MF₆]:Mn⁴⁺, where E is selected from Mg, Ca, Sr, Ba, Zn,        and combinations thereof; and where M is selected from Ge, Si,        Sn, Ti, Zr, and combinations thereof;    -   (G) Ba_(0.65)Zr_(0.35)F_(2.70):Mn⁴⁺; and    -   (H) A₃[ZrF₇]:Mn⁴⁺ where A is selected from Li, Na, K, Rb, Cs,        NH₄; and    -   (I) combinations thereof.        Time, temperature and fluorine-containing oxidizing agents for        the process are described above.

Color stability and quantum efficiency of phosphors annealed in aprocess according to the present invention may be enhanced by treatingthe phosphor in particulate form with a saturated solution of acomposition of formula II

A_(x) [MF_(y)]   II

in aqueous hydrofluoric acid, as described in U.S. Pat. No. 8,252,613.The temperature at which the phosphor is contacted with the solutionranges from about 20° C. to about 50° C. The period of time required toproduce the color stable phosphor ranges from about one minute to aboutfive hours, particularly from about five minutes to about one hour.Concentration of hydrofluoric acid in the aqueous HF solutions rangesfrom about 20% w/w to about 70% w/w, particularly about 40% w/w to about70% w/w. Less concentrated solutions may result in lower yields of thephosphor.

A lighting apparatus or light emitting assembly or lamp 10 according toone embodiment of the present invention is shown in FIG. 1. Lightingapparatus 10 includes a semiconductor radiation source, shown as lightemitting diode (LED) chip 12, and leads 14 electrically attached to theLED chip. The leads 14 may be thin wires supported by a thicker leadframe(s) 16 or the leads may be self supported electrodes and the leadframe may be omitted. The leads 14 provide current to LED chip 12 andthus cause it to emit radiation.

The lamp may include any semiconductor blue or UV light source that iscapable of producing white light when its emitted radiation is directedonto the phosphor. In one embodiment, the semiconductor light source isa blue emitting LED doped with various impurities. Thus, the LED maycomprise a semiconductor diode based on any suitable III-V, II-VI orIV-IV semiconductor layers and having an emission wavelength of about250 to 550 nm. In particular, the LED may contain at least onesemiconductor layer comprising GaN, ZnSe or SiC. For example, the LEDmay comprise a nitride compound semiconductor represented by the formulaIn_(i)Ga_(j)Al_(k)N (where 0≤i; 0≤j; 0≤k and l+j+k=1) having an emissionwavelength greater than about 250 nm and less than about 550 nm. Inparticular embodiments, the chip is a near-uv or blue emitting LEDhaving a peak emission wavelength from about 400 to about 500 nm. SuchLED semiconductors are known in the art. The radiation source isdescribed herein as an LED for convenience. However, as used herein, theterm is meant to encompass all semiconductor radiation sourcesincluding, e.g., semiconductor laser diodes. Further, although thegeneral discussion of the exemplary structures of the inventiondiscussed herein is directed toward inorganic LED based light sources,it should be understood that the LED chip may be replaced by anotherradiation source unless otherwise noted and that any reference tosemiconductor, semiconductor LED, or LED chip is merely representativeof any appropriate radiation source, including, but not limited to,organic light emitting diodes.

In lighting apparatus 10, phosphor composition 22 is radiationallycoupled to the LED chip 12. Radiationally coupled means that theelements are associated with each other so radiation from one istransmitted to the other. Phosphor composition 22 is deposited on theLED 12 by any appropriate method. For example, a water based suspensionof the phosphor(s) can be formed, and applied as a phosphor layer to theLED surface. In one such method, a silicone slurry in which the phosphorparticles are randomly suspended is placed around the LED. This methodis merely exemplary of possible positions of phosphor composition 22 andLED 12. Thus, phosphor composition 22 may be coated over or directly onthe light emitting surface of the LED chip 12 by coating and drying thephosphor suspension over the LED chip 12. In the case of asilicone-based suspension, the suspension is cured at an appropriatetemperature. Both the shell 18 and the encapsulant 20 should betransparent to allow white light 24 to be transmitted through thoseelements. Although not intended to be limiting, in some embodiments, themedian particle size of the phosphor composition ranges from about 1 toabout 50 microns, particularly from about 15 to about 35 microns.

In other embodiments, phosphor composition 22 is interspersed within theencapsulant material 20, instead of being formed directly on the LEDchip 12. The phosphor (in the form of a powder) may be interspersedwithin a single region of the encapsulant material 20 or throughout theentire volume of the encapsulant material. Blue light emitted by the LEDchip 12 mixes with the light emitted by phosphor composition 22, and themixed light appears as white light. If the phosphor is to beinterspersed within the material of encapsulant 20, then a phosphorpowder may be added to a polymer or silicone precursor, loaded aroundthe LED chip 12, and then the polymer precursor may be cured to solidifythe polymer or silicone material. Other known phosphor interspersionmethods may also be used, such as transfer loading.

In some embodiments, the encapsulant material 20 is a silicone matrixhaving an index of refraction R, and, in addition to phosphorcomposition 22, contains a diluent material having less than about 5%absorbance and index of refraction of R±0.1. The diluent material has anindex of refraction of ≤1.7, particularly ≤1.6, and more particularly≤1.5. In particular embodiments, the diluent material is of formula II,and has an index of refraction of about 1.4. Adding an opticallyinactive material to the phosphor/silicone mixture may produce a moregradual distribution of light flux through the phosphor/encapsulantmixture and can result in less damage to the phosphor. Suitablematerials for the diluent include fluoride compounds such as LiF, MgF₂,CaF₂, SrF₂, AlF₃, K₂NaAlF₆, KMgF₃, CaLiAlF₆, K₂LiAlF₆, and K₂SiF₆, whichhave index of refraction ranging from about 1.38 (AlF₃ and K₂NaAlF₆) toabout 1.43 (CaF₂), and polymers having index of refraction ranging fromabout 1.254 to about 1.7. Non-limiting examples of polymers suitable foruse as a diluent include polycarbonates, polyesters, nylons,polyetherimides, polyetherketones, and polymers derived from styrene,acrylate, methacrylate, vinyl, vinyl acetate, ethylene, propylene oxide,and ethylene oxide monomers, and copolymers thereof, includinghalogenated and unhalogenated derivatives. These polymer powders can bedirectly incorporated into silicone encapsulants before silicone curing.

In yet another embodiment, phosphor composition 22 is coated onto asurface of the shell 18, instead of being formed over the LED chip 12.The phosphor composition is preferably coated on the inside surface ofthe shell 18, although the phosphor may be coated on the outside surfaceof the shell, if desired. Phosphor composition 22 may be coated on theentire surface of the shell or only a top portion of the surface of theshell. The UV/blue light emitted by the LED chip 12 mixes with the lightemitted by phosphor composition 22, and the mixed light appears as whitelight. Of course, the phosphor may be located in any two or all threelocations or in any other suitable location, such as separately from theshell or integrated into the LED.

FIG. 2 illustrates a second structure of the system according to thepresent invention. Corresponding numbers from FIGS. 1-4 (e.g. 12 inFIGS. 1 and 112 in FIG. 2) relate to corresponding structures in each ofthe figures, unless otherwise stated. The structure of the embodiment ofFIG. 2 is similar to that of FIG. 1, except that the phosphorcomposition 122 is interspersed within the encapsulant material 120,instead of being formed directly on the LED chip 112. The phosphor (inthe form of a powder) may be interspersed within a single region of theencapsulant material or throughout the entire volume of the encapsulantmaterial. Radiation (indicated by arrow 126) emitted by the LED chip 112mixes with the light emitted by the phosphor 122, and the mixed lightappears as white light 124. If the phosphor is to be interspersed withinthe encapsulant material 120, then a phosphor powder may be added to apolymer precursor, and loaded around the LED chip 112. The polymer orsilicone precursor may then be cured to solidify the polymer orsilicone. Other known phosphor interspersion methods may also be used,such as transfer molding.

FIG. 3 illustrates a third possible structure of the system according tothe present invention. The structure of the embodiment shown in FIG. 3is similar to that of FIG. 1, except that the phosphor composition 222is coated onto a surface of the envelope 218, instead of being formedover the LED chip 212. The phosphor composition 222 is preferably coatedon the inside surface of the envelope 218, although the phosphor may becoated on the outside surface of the envelope, if desired. The phosphorcomposition 222 may be coated on the entire surface of the envelope, oronly a top portion of the surface of the envelope. The radiation 226emitted by the LED chip 212 mixes with the light emitted by the phosphorcomposition 222, and the mixed light appears as white light 224. Ofcourse, the structures of FIGS. 1-3 may be combined, and the phosphormay be located in any two or all three locations, or in any othersuitable location, such as separately from the envelope, or integratedinto the LED.

In any of the above structures, the lamp may also include a plurality ofscattering particles (not shown), which are embedded in the encapsulantmaterial. The scattering particles may comprise, for example, alumina ortitania. The scattering particles effectively scatter the directionallight emitted from the LED chip, preferably with a negligible amount ofabsorption.

As shown in a fourth structure in FIG. 4, the LED chip 412 may bemounted in a reflective cup 430. The cup 430 may be made from or coatedwith a dielectric material, such as alumina, titania, or otherdielectric powders known in the art, or be coated by a reflective metal,such as aluminum or silver. The remainder of the structure of theembodiment of FIG. 4 is the same as those of any of the previousfigures, and can include two leads 416, a conducting wire 432, and anencapsulant material 420. The reflective cup 430 is supported by thefirst lead 416 and the conducting wire 432 is used to electricallyconnect the LED chip 412 with the second lead 416.

Another structure (particularly for backlight applications) is a surfacemounted device (“SMD”) type light emitting diode 550, e.g. asillustrated in FIG. 5. This SMD is a “side-emitting type” and has alight-emitting window 552 on a protruding portion of a light guidingmember 554. An SMD package may comprise an LED chip as defined above,and a phosphor material that is excited by the light emitted from theLED chip. Other backlight devices include, but are not limited to, TVs,computers, smartphones, tablet computers and other handheld devices thathave a display including a semiconductor light source; and a colorstable Mn⁴⁺ doped phosphor according to the present invention.

When used with an LED emitting at from 350 to 550 nm and one or moreother appropriate phosphors, the resulting lighting system will producea light having a white color. Lamp 10 may also include scatteringparticles (not shown), which are embedded in the encapsulant material.The scattering particles may comprise, for example, alumina or titania.The scattering particles effectively scatter the directional lightemitted from the LED chip, preferably with a negligible amount ofabsorption.

In addition to the color stable Mn⁴⁺ doped phosphor, phosphorcomposition 22 may include one or more other phosphors. When used in alighting apparatus in combination with a blue or near UV LED emittingradiation in the range of about 250 to 550 nm, the resultant lightemitted by the assembly will be a white light. Other phosphors such asgreen, blue, yellow, red, orange, or other color phosphors may be usedin the blend to customize the white color of the resulting light andproduce specific spectral power distributions. Other materials suitablefor use in phosphor composition 22 include electroluminescent polymerssuch as polyfluorenes, preferably poly(9,9-dioctyl fluorene) andcopolymers thereof, such aspoly(9,9′-dioctylfluorene-co-bis-N,N′-(4-butylphenyl)diphenylamine)(F8-TFB); poly(vinylcarbazole) and polyphenylenevinylene and theirderivatives. In addition, the light emitting layer may include a blue,yellow, orange, green or red phosphorescent dye or metal complex, or acombination thereof. Materials suitable for use as the phosphorescentdye include, but are not limited to, tris(1-phenylisoquinoline) iridium(III) (red dye), tris(2-phenylpyridine) iridium (green dye) and Iridium(III) bis(2-(4,6-difluorephenyl)pyridinato-N,C2) (blue dye).Commercially available fluorescent and phosphorescent metal complexesfrom ADS (American Dyes Source, Inc.) may also be used. ADS green dyesinclude ADS060GE, ADS061GE, ADS063GE, and ADS066GE, ADS078GE, andADS090GE. ADS blue dyes include ADS064BE, ADS065BE, and ADS070BE. ADSred dyes include ADS067RE, ADS068RE, ADS069RE, ADS075RE, ADS076RE,ADS067RE, and ADS077RE.

Suitable phosphors for use in phosphor composition 22 include, but arenot limited to:

((Sr_(1−z) (Ca, Ba, Mg, Zn)_(z))_(1−(x+w))(x+w)(Li, Na, K,Rb)_(w)Ce_(x))₃(Al_(1−y)Si_(y))O_(4+y+3(x−w))F_(1−y−3(x−w)), 0<x≤0.10,0≤y≤0.5, 0≤z≤0.5, 0≤w≤x,(Ca, Ce)₃Sc₂Si₃O₁₂(CaSiG);(Sr,Ca,Ba)₃Al¹⁻,Si_(x)O_(4+x)F_(1−x):Ce³⁺ (SASOF));(Ba,Sr,Ca)₅(PO₄)₃(Cl,F,Br,OH):Eu²⁺,Mn²⁺; (Ba,Sr,Ca)BPO₅:Eu²⁺,Mn²⁺;(Sr,Ca)₁₀(PO₄)₆*νB₂O₃:Eu²⁺ (wherein 0≤ν≤1); Sr₂Si₃O₈*2SrCl₂:Eu²⁺;(Ca,Sr,Ba)₃MgSi₂O₈:Eu²⁺,Mn²⁺; BaAl₈O₁₃:Eu²⁺;2SrO*0.84P₂O₅*0.16B₂O₃:Eu²⁺;(Ba,Sr,Ca)MgAl₁₀O₁₇:Eu²⁺,Mn²⁺; (Ba,Sr,Ca)Al₂O₄:Eu²⁺;(Y,Gd,Lu,Sc,La)BO₃:Ce³⁺,Tb³⁺;ZnS:Cu⁺,Cl⁻; ZnS:Cu+,Al³⁺; ZnS:Ag⁺,Cl⁻; ZnS:Ag⁺,Al³⁺;(Ba,Sr,Ca)₂Si_(1−ξ)O_(4-2ξ):Eu²⁺ (wherein 0≤ξ≤0.2);(Ba,Sr,Ca)₂(Mg,Zn)Si₂O₇:Eu²⁺; (Sr,Ca,Ba)(Al,Ga,In)₂S₄:Eu²⁺;(Y,Gd,Tb,La,Sm,Pr,Lu)₃(Al,Ga)_(5-α)O_(12−3/2α):Ce³⁺ (wherein 0≤α≤0.5);(Ca,Sr)₈(Mg,Zn)(SiO₄)₄Cl₂:Eu²⁺,Mn²⁺; Na₂Gd₂B₂O₇:Ce³⁺,Tb³⁺;(Sr,Ca,Ba,Mg,Zn)₂P₂O₇:Eu²⁺,Mn²⁺;(Gd,Y,Lu,La)₂O₃:Eu³⁺,Bi³⁺; (Gd,Y,Lu,La)₂O₂S:Eu³⁺,Bi³⁺;(Gd,Y,Lu,La)VO₄:Eu³⁺,Bi³⁺; (Ca,Sr)S:Eu²⁺,Ce³⁺; SrY₂S₄:Eu²⁺;CaLa₂S₄:Ce³⁺; (Ba,Sr,Ca)MgP₂O₇:Eu²⁺,Mn²⁺; (Y,Lu)₂WO₆:Eu³⁺,Mo⁶⁺;(Ba,Sr,Ca)_(β)Si_(γ)N_(μ):Eu²⁺ (wherein 2β+4γ=3μ); Ca₃(SiO₄)Cl₂:Eu²⁺;(Lu,Sc,Y,Tb)_(2−u−v)Ce_(v)Ca_(1−u)Li_(w)Mg_(2−w)P_(w)(Si,Ge)_(3−w)O_(12−u/2)(where −0.5≤u≤1, 0<v≤0.1, and 0≤w≤0.2);(Y,Lu,Gd)_(2−μ)Ca_(μ)Si₄N_(6+μ)C_(1−μ):Ce³⁺, (wherein 0≤μ≤0.5);(Lu,Ca,Li,Mg,Y), α-SiAlON doped with Eu²⁺ and/or Ce³⁺;(Ca,Sr,Ba)SiO₂N₂:Eu²⁺,Ce³⁺; μ-SiAlON:Eu²⁺, 3.5MgO*0.5MgF₂*GeO₂:Mn⁴⁺;Ca_(1−c−f)Ce_(c)Eu_(f)Al_(1+c)Si_(1−c)N₃, (where 0≤c≤0.2, 0≤f≤0.2);Ca_(1−h−r)Ce_(h)Eu_(r)Al_(1−h)(Mg,Zn)_(h)SiN₃, (where 0≤h≤0.2, 0≤r≤0.2);Ca_(1−2s−t)Ce_(s)(Li,Na)_(s)Eu_(t)AlSiN₃, (where 0≤s≤0.2, 0≤f≤0.2,s+t>0); and Ca_(1−σ−χ−ϕ)Ce_(σ)(Li,Na)_(χ)Eu_(ϕ),Al_(1+σ−χ)Si_(1−σ+χ)N₃,(where 0≤σ≤0.2, 0≤χ≤0.4, 0≤ϕ≤0.2).

The ratio of each of the individual phosphors in the phosphor blend mayvary depending on the characteristics of the desired light output. Therelative proportions of the individual phosphors in the variousembodiment phosphor blends may be adjusted such that when theiremissions are blended and employed in an LED lighting device, there isproduced visible light of predetermined x and y values on the CIEchromaticity diagram. As stated, a white light is preferably produced.This white light may, for instance, may possess an x value in the rangeof about 0.20 to about 0.55, and a y value in the range of about 0.20 toabout 0.55. As stated, however, the exact identity and amounts of eachphosphor in the phosphor composition can be varied according to theneeds of the end user. For example, the material can be used for LEDsintended for liquid crystal display (LCD) backlighting. In thisapplication, the LED color point would be appropriately tuned based uponthe desired white, red, green, and blue colors after passing through anLCD/color filter combination.

LED devices incorporating the color stable phosphors and used forbacklighting or general illumination lighting may have a color shift of<1.5 MacAdam ellipses over 2,000 hours of device operation, and, inparticular embodiments, <1 MacAdam ellipse over 2,000 hours, where thephosphor/polymer composite is in direct contact with the LED chipsurface, LED wall plug efficiency greater than 40%,and LED currentdensities are greater than 2 A/cm². In accelerated testing, where thephosphor/polymer composite is in direct contact with the LED chipsurface, LED wall plug efficiency greater than 18%, and LED currentdensities are greater than 70 A/cm², LED devices may have color shift of<1.5 MacAdam ellipse over 30 minutes.

The color stable Mn⁴⁺ doped phosphors of the present invention may beused in applications other than those described above. For example, thematerial may be used as a phosphor in a fluorescent lamp, in a cathoderay tube, in a plasma display device or in a liquid crystal display(LCD). The material may also be used as a scintillator in anelectromagnetic calorimeter, in a gamma ray camera, in a computedtomography scanner or in a laser. These uses are merely exemplary andnot limiting.

Examples General Procedures Silicone Tape Sample Preparation

Samples were prepared by mixing 500 mg of the material to be tested with1.50 g silicone (Sylgard 184). The mixture was degassed in a vacuumchamber for about 15 minutes. The mixture (0.70 g) was poured into adisc-shaped template (28.7 mm diameter and 0.79 mm thick) and baked for30 minutes at 90° C. The sample was cut into squares of sizeapproximately 5 mm×5 mm for testing.

Stability Testing High Light Flux Conditions

A laser diode emitting at 446 nm was coupled to an optical fiber with acollimator at its other end. The power output was 310 mW and the beamdiameter at the sample was 700 microns. This is equivalent to a flux of80 W/cm² on the sample surface. The spectral power distribution (SPD)spectrum that is a combination of the scattered radiation from the laserand the emission from the excited phosphor is collected with a 1 meter(diameter) integrating sphere and the data processed with thespectrometer software (Specwin). At intervals of two minutes, theintegrated power from the laser and the phosphor emission were recordedover a period of about 21 hours by integrating the SPD from 400 nm to500 nm and 550 nm to 700 nm respectively. The first 90 minutes of themeasurement are discarded to avoid effects due to the thermalstabilization of the laser. The percentage of intensity loss due tolaser damage is calculated as follows:

${{Intensity}\mspace{14mu} {loss}\mspace{14mu} (\%)} = {100\frac{( {{Power} - {{Initial}\mspace{14mu} {power}}} )}{{Initial}\mspace{14mu} {power}}}$

While only the emitter power from the phosphor is plotted, theintegrated power from the laser emission as well as its peak positionwas monitored to ensure that the laser remained stable (variations ofless than 1%) during the experiment.

High Temperature High Humidity (HHTH) Treatment

Samples for high temperature, high humidity (HTHH) treatment were madeby mixing phosphor powders into a two-part methyl silicone binder(RTV-615, Momentive Performance Materials) in a ratio of 0.9 g phosphorto 0.825 g silicone (parts A+B). The phosphor/silicone mixture is thenpoured into aluminum sample holders and cured at 90° C. for 20 minutes.Control samples were stored under nitrogen, and samples for exposure toHTHH conditions were placed into a 85° C./85% RH controlled atmospherechamber. These HTHH samples are periodically removed and theirluminescence intensity under 450 nm excitation compared to that of thecontrol samples.

Examples 1-12 Annealing Under Fluorine Atmosphere Procedure

A Mn-doped potassium fluorosilicate (PFS:Mn) precursor, K₂SiF₆:Mn,containing 0.68 wt % Mn, based on total weight of the precursor materialwas placed in a furnace chamber. The furnace chamber was evacuated andwas filled with an atmosphere containing fluorine gas and nitrogen gas.The chamber was then heated to the desired anneal temperature. Afterholding for the desired amount of time, the chamber was cooled to roomtemperature. The fluorine nitrogen mixture was evacuated, the chamberwas filled and purged several times with nitrogen to ensure the completeremoval of fluorine gas before opening the chamber.

For Examples 1-5, the atmosphere in the chamber was composed of 20%fluorine gas and 80% nitrogen gas. For Example 6, the atmosphere wascomposed of 5% fluorine gas and 95% nitrogen gas. Furnace setpointtemperature and time for a first annealing period (T1 and t1) andfurnace setpoint temperature and time for a second annealing period, ifany, (T2 and t2) are indicated in Table 1. Due to the furnace setup andhow the sample is placed relative to the control thermocouples in thefurnace actual sample temperatures in the furnace were 25-75° C. higherthan the furnace setpoint.

The stability of precursor PFS:Mn having wt % Mn ranging from 0.68-0.73wt % and the product phosphor (Comparative Example 1) was tested underconditions of high light flux, and results are shown in Table 1. Theannealed materials experienced significantly less damage than thematerials that were not heat treated.

TABLE 1 Example T1 t1 T2 t2 Laser No. (° C.) (hr.) (° C.) (hr.) DamageComments Comp. — — — — 6%-9% No heat treatment Ex. 1 1 225 4 — — 3.8% 2225 4 350 4 1.8% Post-treatment 3 300 4 425 4 0.8% 4 350 4 — — 2.7% 5425 4 — — 1.1% 6 225 4 350 4 2.5% 5% F₂ and 95% N₂

Example 2 Post-Treatment of Annealed Phosphor

The annealed PFS phosphor powder from Example 2 was treated with asaturated solution of K₂SiF₆ by placing the powder (˜10 g) in a Teflonbeaker containing 100 mL of a saturated solution of K₂SiF₆ (initiallymade by adding ˜17 g of K₂SiF₆ in 40% HF at room temperature, stirring,and filtering the solution). The suspension was stirred slowly, and theresidue is filtered and dried under vacuum. Further removal of HF fromthe dried filtrate was done by washing in acetone 3-5 times and heatingthe filtrate to 100° C. for 10 min. Stability of the post-treatedphosphor along with a sample of PFS that was not annealed but was posttreated was evaluated under HHTH conditions, at 85° C./85% RH for 620hours. The post-treated sample experienced less degradation under thehigh temperature/humidity conditions, maintaining about 94% emissionintensity, while the non-annealed sample maintained about 86% emissionintensity.

Comparative Examples 2-7

Samples of unannealed and untreated PFS precursors having Mn contentranging from 0.5-0.85 wt % were tested under conditions of high lightflux as shown in Table 2.

Examples 7-12

Samples of the PFS precursors were annealed at furnace setpointtemperatures ranging from 425-550° C. for times ranging from 4-8 hoursas shown in Table 2. After annealing, all samples were treated insaturated K₂SiF₆ solutions in 48% HF as in Example 2. The annealedphosphors were tested under conditions of high light flux, and resultsare shown in Table 2.

TABLE 2 Mn Laser level Furnace setpoint damage/% intensity Example no.(wt %) T, ° C. Time loss Comp. Ex. 2 0.74% N/A 6.9% 7 500 8 hours 1.5%Comp. Ex. 3 0.84% N/A 10.9%  8 500 8 hours 2.3% Comp. Ex. 4 0.68% N/A7.1% 9 475 8 hours 1.0% Comp. Ex. 5 0.73% N/A 8.4% 10 500 8 hours 1.25% Comp. Ex. 6 0.71% N/A 9.9% 11 475 8 hours 1.1% Comp. Ex. 7 0.53% N/A3.3% 12 425 4 hours 0.6%

Example 13 Diluted PFS Silicone Tape

Unannealed K₂SiF₆:Mn (0.68 wt % Mn) was mixed with a silicone precursorand formed into a solid tape composed of 87.8 volume % silicone and 12.2volume % PFS. A control contained a 1:1 mixture of K₂SiF₆:Mn (0.68 wt %Mn) (doped PFS) and K₂SiF₆ (0 wt % Mn) (undoped PFS), having a finalcomposition of 75.6 vol % silicone, 12.2% undoped PFS and 12.2 vol %doped PFS.

The tape was subjected to stability testing under high light fluxconditions. Power intensity loss for the diluted PFS sample was about2.5% after 24 hours, and was significantly lower than that of thecontrol.

Example 14 Reduced Mn Level

A Mn-doped potassium fluorosilicate (PFS:Mn) precursor, K₂SiF₆:Mn,containing 0.53 wt % Mn, based on total weight of the precursor materialwas tested under conditions of high light flux, and results are shown inTable 3. The material containing the lower Mn level experiencedsignificantly less damage than the control that was not heat treated(Comparative Example 8).

TABLE 3 Example Laser Damage % Mn Comments Comp. Ex. 8 6%-9% 0.68-0.73Not annealed 14 3.4% 0.53 Mn⁴⁺ reduced by 25%

Example 15 Higher Annealing Temperatures in an Alternate Furnace

A Mn-doped potassium fluorosilicate (PFS:Mn) precursor, K₂SiF₆:Mn,containing 0.84 wt % Mn, based on total weight of the precursor materialwas annealed under the conditions shown in Table 4 in a differentfurnace whose setpoint temperatures were closer to the maximumtemperature in the furnace. After the annealing step, the materials wereprocessed using the post-treatment process in Example 2. The phosphorand an annealed, untreated sample (Comparative Example 9) were testedunder conditions of high light flux. Results are shown in Table 4. Theannealed and post-treated material experienced significantly less damagethan the control that was not heat treated. In addition, the phosphorquantum efficiency under blue LED excitation was higher by 7.5% versusthe initial control sample.

TABLE 4 Relative quantum Example Laser Damage efficiency % Mn ConditionsComp. 10.9% 100 0.84% Not annealed Ex. 9 15 1.5% 107.5 0.82% 540° C. in10 psia of 20% F₂/80% N₂ for 8 hours

Examples 16 and 17 LED Packaging and Testing Procedure

LED packages were made using K₂SiF₆:Mn⁴⁺ phosphors that were annealedusing the conditions in examples 2 (Example 16) and 5 (Example 17) aswell as unannealed K₂SiF₆:Mn⁴⁺ phosphors (Comparative Examples 10 and11). These phosphors were blended with Ce³⁺-doped garnets and a siliconebinder and deposited within a package similar to typical 3030 LEDpackage with two blue emitting LED chips for a color temperature of˜4000K. The packages were then attached to a printed circuit board. TheLED dimensions in these packages were approximately 0.65 mm×0.65 mm;taking this LED area, the LED current density is defined as: LED currentdensity=Drive current/[(LED area)*(number of LEDs in package)]

The devices of Comparative Example 10 and Example 16 were operated at 30mA, at ambient temperature (T_(ambient)) of 47° C. for 4000 hours. Thedevices of Comparative Example 11 and Example 17 were operated at 700 mAdrive current at a board temperature (T_(board)) of 60° C. for 30minutes. Using the above formula, a 30 mA drive current gives a LEDcurrent density of approximately 3.6 A/cm², and a 700 mA drive currentgives a LED current density of approximately 83 A/cm². Similar LEDpackages without phosphors give a wall-plug efficiency (defined byemitted optical power divided by input electrical power) of 54% at 100mA drive current and board temperature of 60° C. and 22% at 700 mA drivecurrent and board temperature of 60° C. The device color point wasobtained by measuring the spectral power distribution of the LED deviceusing a calibrated integrating sphere spectrometer at different timesafter LED operation under different drive current and ambient/boardtemperature conditions. Results are shown in Tables 5 and 6.

TABLE 5 MacAdam Dx after Dy after steps after 4000 4000 D[intensity@631nm] Example no. 4000 hours hours hours after 4000 hours Comp. Ex. 101.82 0.0023 0.0010 91.7% 16 0.91 0.0004 0.0000 93.5%

TABLE 6 MacAdam D[I (631 nm)/ steps after Dx after I (455 nm)] afterExample no. 30 min 30 min Dy after 30 min 30 min Comp. 4.0 −0.0058−0.0012 −10.5% Ex. 11 17 0.5 −0.0011 −0.0009 −1.3%

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

1-9. (canceled)
 10. A lighting apparatus comprising a semiconductorlight source in direct contact with a polymer composite comprising acolor stable Mn⁴⁺ doped phosphor, wherein the lighting apparatus has acolor shift of ≤1.5 MacAdam ellipses after operating for at least 2,000hour at a LED current density greater than 2 A/cm², a LED wall-plugefficiency greater than 40%, and a board temperature greater than 25° C.wherein the color stable Mn⁴⁺ doped phosphor is K₂SiF₆:Mn⁴⁺.
 11. Alighting apparatus according to claim 10, wherein the MacAdam ellipsecolor shift is ≤1.